It is known to use a varistor as overvoltage protection element. The varistor is connected to the supply voltage in parallel with a device to be protected. If an overvoltage event occurs, the varistor becomes conductive and conducts the overvoltage past the device to be protected.
However, varistors are subject to aging processes. One aging process results from a large number of discharges, and another aging process occurs as a result of the strength and duration of a discharge process. Thermal processes play a special role here. The two abovementioned aging processes occur at different speeds. In particular, in the latter aging process, there is a risk of breakdown, i.e., of a short circuit-like connection occurring, that can result in the explosion-like destruction of the varistor due to the high energy conversion. This explosive destruction can lead to fires in addition to the explosion effect.
Disconnectors are therefore usually provided in order to protect varistors from thermal overload. These disconnectors are usually based on a mechanically biased connector that is connected with a solder to the varistor. If the varistor heats up excessively, the solder softens and the biased connector moves away, disconnecting the electrical connection.
However, it is often found that, in the event of high energy conversions, separation is no longer possible with conventional disconnectors.
However, it would be desirable to provide an overvoltage protection device that safely disconnects even in the case of high energy conversions.